a) Field of the Invention
This invention generally relates to suspension and drive systems of motorcycles and, more particularly, to swing arm assemblies of such suspension systems and such drive systems that include an endless belt positioned through the swing arm and used to transmit rotational power from the motorcycle's engine to a rear wheel.
b) Description of the Prior Art
There are three main types of drive systems of today's motorcycles, that is, three different ways to transfer the rotational torque from the crank of the motorcycle's engine to the motorcycle's rear wheel; by drive chain, rotatable drive shaft, or endless toothed drive belt. Although each of these drive systems includes advantages, they are not without problems.
The earliest and probably most widely used drive system is the drive chain. The drive chain of a motorcycle is similar in construction to a standard bicycle chain. The motorcycle chain is made from pivotally connected linking elements, each of which rotatably supports an intermediate contact sleeve. The contact sleeves of the drive chain engage the teeth of the motorcycle's drive sprockets, one sprocket is mounted to the crank at the engine, the other is attached to the rear wheel. Although the drive chain provides a strong and low cost method of transmitting drive torque to the rear wheel of a motorcycle, being made from metal, the chain is heavy and must be kept well lubricated throughout its service life. Another problem with using a chain as a drive component is that as the individual links engage and disengage the two sprockets of the motorcycle, they make noise. One benefit with using the drive chain, however, is that should the chain require removal from the motorcycle, two adjacent connecting links may be simply detached from each other by removing a press-fit connecting pin.
More and more motorcycles are using drive belts to drive the rear wheel. The drive belt is a flexible endless belt made from various materials including rubber plastic and reinforcing fibers. The belt is molded as a single, endless piece and includes integrally molded teeth which engage appropriately sized and shaped toothed pulleys (in place of the sprockets in the above-described chain version). The belt has the advantages of being very quiet as it drives the rear wheel of a motorcycle, and does not require lubrication. However, a problem with using such an endless belt to drive a motorcycle is that it will wear more quickly than a chain and typically must be periodically replaced.
Both the chain and the belt are connected between the motorcycle's engine and its rear wheel, typically passing between members of a swing arm assembly. The swing arm assembly is a sub-frame that directly supports the rear wheel. The swing arm is pivotally attached to the main frame and includes a suspension spring and usually a shock absorber located between it and the main frame. Typically, the construction of the swing arm assembly (with an attached wheel) "closes" the belt or chain within the swing arm assembly and prevents its quick and easy removal from the swing arm assembly. Of course, as described above, the chain may be disassembled and thereby removed from the swing arm. However, if an endless belt is used, the entire swing arm assembly must first be removed.
The swing arm assembly of most motorcycles includes a bushing which aligns with and is pivotally attached to a mating bushing (or two opposing bushings) of the main frame of the motorcycle. The swing arm assembly is pivotally attached to the main frame using a bolt (or opposing bolts) positioned along the aligned bushings, defining a pivot axis. These bolts must be removed to detach the swing arm assembly from the main frame of the motorcycle. Furthermore, since the swing arm assembly is under a spring bias from the suspension spring, it is likely that the suspension components must be removed prior to detaching the swing arm assembly from the main frame.
Although possible to accomplish the removal of the swing arm assembly and the suspension components, and ultimately, the endless belt, this procedure is complex and time consuming, and cannot be easily performed when traveling, such as if an endless belt breaks or otherwise requires replacement at a remote location.
It is therefore an object of the invention to provide a swing arm assembly pivotally connected to a main frame of a motorcycle along a pivot axis which includes means to remove an endless drive belt past the pivot axis without detaching the swing arm assembly from the main frame and without detaching any of the suspension components of the motorcycle.
It is another object of the invention to provide a swing arm assembly which overcomes the deficiencies of the prior art.